Oil companies are facing new rancour in the US today after Exxon Mobil reported a quarterly profit of $11.7bn, the largest in American history.

That stunning figure – equivalent to a profit of $1,486 per second – elicited harsh condemnations from Barack Obama and his fellow Democrats, who wasted no time in accusing John McCain of protecting cash-rich oil companies while fuel prices rise.

"Perhaps the only thing more outrageous than Exxon Mobil making record profits while Americans are paying record prices at the pump is the fact that Senator McCain has proposed giving them an additional $1.2bn tax break," Obama said in a statement.

"Instead of an energy policy that reads like an oil-company wish list, it's time to create a new American energy economy by investing in alternative energy, creating millions of new jobs, increasing fuel efficiency standards, and ending the tyranny of oil once and for all."

Four senior Democrats in Congress called a press conference today to lambaste the largest US oil companies for spending more on stock buy-backs to enrich shareholders than on energy exploration.

In the first quarter of this year, Exxon spent $8.8m on repurchasing its own stock and $5.5bn on exploration. Despite its history-making profit in the second quarter, Wall Street analysts had expected a bigger haul from the company and its shares fell today in early trading hours.

"[D]oes the oil and gas industry really need more tax breaks and more public land?" asked a fact sheet on Exxon profits released by Democrat Nancy Pelosi, leader of the House of Representatives.

Democrats have struggled for a political advantage on energy in recent weeks as their past emphasis on alternative sources such as solar and wind gives way to a raucous debate over expanding domestic drilling.

Republicans believe they have found a winning issue in pushing for expanded offshore drilling to stem the steady increase in gas prices this year, particularly after presidential nominee John McCain changed his stance to support new oil exploration along the coasts.

Yet the Exxon profits, in addition to the $11.6bn netted by Royal Dutch Shell and a $5.4bn take for Conoco Philips, could offer Democrats an opening for a new populist attack on the oil industry.

Party leaders already have taken some credit for this week's slight dip in oil prices, although Republicans blocked their proposals to require Exxon and competitors to drill on land they already lease before new offshore areas are opened.

"[Democrats] have been taking action, and we think that has had a psychological effect – even though, unfortunately, Republicans have thwarted the passage of some of these pieces of legislation," Democrat Steny Hoyer, No 2 leader in the House, told reporters yesterday.